1. Technical Field
The present invention relates to magnetic read and write heads. More particularly, the present invention relates to a planar silicon head having a magnetoresistive element associated with a read gap, and having a separate write gap.
2. Description of the Prior Art
The level of recording medium noise in a magnetic recording is generally larger at the edges of a recorded track than in the center of the track. Therefore, it is desirable to provide a magnetic head having a read width that is somewhat narrower than the write track width. A narrower read head, when positioned toward the center of a recorded track, only senses information from the center of the track and not the noise at the edges of the track. Providing a wider write track width also ensures the complete erasure of old data and the rewriting of a new track that is wide enough to avoid subsequent reading of the old data at the track edges due to servo tracking error. This makes for good overwrite performance. Magnetoresistive ("MR") heads having inductive write gaps that are separate from the MR read gaps are known. Separation of the read and write gaps allows the two gaps to be individually optimized. Typically, MR heads have an inductive write gap that is longer than the read gap, and a write track width that is wider than the read track width, See, for example C. Tsang et. al., Gigabit Density Recording using Dual-Element MR/Inductive Heads on Thin-Film Disks, IEEE Trans. Mag., Vol. 26, No. 5 (September 1990).
Known dual gap MR heads have one edge of the magnetoresistive element ("MRE") exposed to the head air bearing surface ("ABS"). As such, the MRE is subjected to excessive wear, and is prone to shorting and corrosion. Magnetoresistive heads also have an asymmetric cross-track profile that complicates servo design. See, for example T. C. Anthony et al, Dual Stripe Magnetoresistive Heads for High Density Recording, IEEE Trans. Mag., Vol. 30, No. 2 (to be published March 1994).
In the patent application, V. W. Hesterman, M. K. Bhattacharyya A Planar Magnetoresistive Head, Ser. No. 08/146,255, filed Nov. 1, 1993, and commonly assigned to Hewlett-Packard Company, which discloses a silicon planar head, an MRE is located across the head gap for reading. In such a head, the thin-film MRE is located away from the ABS by bridging the MRE across the gaps of a magnetic yoke. The magnetic yoke includes a write coil for writing, and the MRE reads information. During manufacture of the head, the yoke is formed from a thin-film ferromagnetic material deposited in a cavity formed in a substrate. The thin-film MRE is positioned across the gap on the side of the yoke opposite the air bearing surface. This arrangement, of positioning the MRE away from the ABS, solves the problems of excessive wear and corrosion of the MRE, and also eliminates the asymmetric nature of the cross-track response. However, in this design the same gap performs both the reading and writing operations, and consequently the read and write track widths are identical. The construction process for an inductive version of a planar silicon head is described in J. P Lazzari, Planar Structure Thin Film Magnetic Head, U.S. Pat. No. 4,949,207 (Aug. 14, 1990).
It would be advantageous if separate read and write gaps could also be incorporated into a planar silicon magnetoresistive head.